Multi-speed recording for multi-layer disc

ABSTRACT

The present invention relates to a recording apparatus, record carrier and method of recording data on at least two layers of a recording medium by using a radiation power, wherein individual recording speeds are determined for respective ones of the at least two layers at different values of the radiation power. A recording speed to be used for recording on an individual one of the at least two recording layers is selected based on a maximum radiation power specified for the recording operation, and the speed of the recording operation is controlled individually for each of the at least two layers based on the selected recording speed. The determination of the individual recording speeds at different radiation power values may be written or embossed on the record carrier. Furthermore, a recording sequence used for recording on the recording layers can be set based on the sensitivities and thus recording speeds. Thereby, total recording time can be minimized for multi-layer recording media.

This is a continuation of prior application Ser. No. 11/569,075, nowU.S. Pat. No. 7,903,512, filed Nov. 14, 2006 which is a National Stageof International Application PCT/IB2005/051516 filed May 10, 2005, whichclaimed foreign priority benefit of EP application EP04102146 filed May17, 2004 and which are all incorporated herein in whole by reference.

The present invention relates to a recording apparatus and power controlmethod of controlling a radiation power used for recording data on arecording medium, and to a record carrier to which information can bewritten using the recording apparatus and power control method.

Optically recordable record carriers or information carriers aregenerally known and are used in recording apparatuses which record dataon the information carrier by means of a radiation beam, e.g., a laserbeam. The radiation beam is focused onto a recording layer in theinformation carrier. In the case of an adequate radiation beam intensityor radiation power, the optical properties of the recording layer at thelocation of the focal spot will change, as a result of which a mark isproduced in the recording layer. By varying the radiation beamintensity, a pattern of marks can be formed in the recording layer. Therecorded pattern contains the data to be recorded in coded form.Examples of such an optically recordable information carrier are theCD-R (Compact Disc Recordable) or CD-RW (Compact Disc Rewritable) or theDVD-R (Digital Versatile Disc Recordable) or the related DVD+R.

In order to extend the storage capacity of optically recordableinformation carriers, information carriers have been introduced whichcomprise a plurality of superposed recording layers. The recordinglayers of such multi-layer information carriers can be of a read-onlyand/or recordable (i.e. write-once) and/or rewritable type. Eachrecording layer in a multi-layer optically recordable informationcarrier can be inscribed separately by focusing the radiation beam ontothe relevant recording layer. The recording apparatuses use a highNumerical Aperture (NA). Owing to this high NA, the diameter of theradiation beam at the location of the recording layers situated betweenthe source of the radiation beam (e.g., laser light source) and therecording layer to be inscribed (intermediate layers) is comparativelylarge. As a result of this, the intensity of the laser beam at thelocation of the intermediate layers will be inadequate intensity toproduce marks on these layers, whereas producing marks on the recordinglayer to be inscribed is possible. Also, at the location of each of therecording layers having a distance between the respective layer and theradiation source which is larger than the distance between the recordinglayer to be inscribed and the radiation source, the intensity of theradiation beam is inadequate to produce marks in these layers owing tothe comparatively large diameter of the beam.

However, although the intermediate layers cannot be inscribed, they haveinfluence on the radiation beam. A part of the radiation beam will bereflected, diffused, and absorbed by the intermediate layers. Theremainder of the radiation beam, quantified by the transmissioncoefficient, will be transmitted by the intermediate layers. Themagnitude of the transmitted part depends on the optical properties ofthe intermediate layers. However, these optical properties change whenthese layers are inscribed. The intensity of the radiation beam shouldthus be so high that in all cases each recording layer in themulti-layer optically recordable information carrier can be inscribed.

Typically, the required radiation power to inscribe or record data on arecordable or rewritable layer in a multi-layer medium will be largerthan the required power in a single-layer medium. The top layer(s) haveto be semi-transparent and become less sensitive due to a lowerabsorption of the radiation beam. The bottom layer(s) are shielded bythe top layer(s) and therefore require a higher radiation power.

A recording apparatus such as an optical storage drive has a maximumlaser power. If, at a given recording speed, the sensitivity of arecordable or rewritable recording layer is such that it requires morethan the maximum laser power, data can only be recorded at a lowerspeed. Consequently, the total time required to record a multi-layermedium, containing n recordable and/or rewritable layers, may be morethan n times the total recording time of a single-layer medium.Therefore, it is important to develop a recording scheme which minimizesthe total recording time.

It is an object of the present invention to provide an improvedrecording scheme by means of which recording time of multi-layerrecording media can be reduced.

This object is achieved by a recording apparatus as claimed in claim 1,by a recording method as claimed in claim 7, and by a record carrier asclaimed in claim 9.

Accordingly, recording time can be reduced by selecting and settingspecific recording speeds for individual recording layers based on thedetermined individual recording speeds for each recording layer. The toplayers which require less radiation power can thus be recorded at ahigher recording speed due to the lower radiation power required forrecording.

The determination means may be arranged to derive the individualrecording speeds from a control information read from the recordingmedium. The individual recording speeds may be derived directly from thecontrol information, e.g. based on discrete number(s) or the like.Alternatively, the individual recording speeds may be derived based onan interpolation or extrapolation of the control information, e.g., aninterpolation or extrapolation of discrete numbers stored on therecording medium, to thereby provide a better adaptation of the selectedrecording speed. In particular, the control information may bepre-stored in a pre-groove of the recording medium. Thereby, theindividual recording speeds and their related writing powers can bedirectly read from the recording medium without requiring dedicatedlook-up tables or other memory means for storing the control informationof each possible type of multi-layer recording medium.

Furthermore, the selection means may be arranged to select the highestallowable recording speed for each individual one of the at least tworecording layers. This leads to an optimization of recording speeds ofeach individual recording layer to achieve a minimized recording time.

The speed control means can be arranged to perform recording at aselected higher speed in a first layer of the at least two layers, andto perform recording at a selected lower speed on a second layer of theat least two recording layers. The first layer may be a top layer andthe second layer may be a bottom layer of the recording medium, or viceversa.

In general, the speed control means may be arranged to determine arecording sequence of the at least two layers based on determinedsensitivities of the at least two layers. The sensitivities may bedetermined on the basis of the selected recording speeds or,alternatively, by the determination means from a control informationread from the recording medium. Such a determination of the recordingsequence based on the layer sensitivities is particularly advantageousfor multi-layer recording media with three or more recording layers, asit leads to an increased overall recording speed.

The present invention will now be described on the basis of preferredembodiments with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic block diagram of a recording apparatusaccording to the preferred embodiments;

FIG. 2 shows a schematic side view of a record carrier according to thepreferred embodiments with an indication of the control informationprovided thereon; and

FIG. 3 shows a schematic flow diagram of a recording method according tothe first preferred embodiment.

In the following the preferred embodiments will be described withrespect to an optical drive or optical disc recorder for a multi-speedand multi-layer recordable and/or rewritable optical storage medium,such as a multi-layer disc selected from the group of optical discsconsisting of dual-layer DVD+R, dual-layer DVD+RW, dual-layer DVD-R anddual-layer DVD-RW.

The DVD+R/+RW format is becoming increasingly popular for digital videorecording as well as for all PC (Personal Computer) data storageapplications. A key advantage of the DVD+R/+RW format over competitiveformats is its backward compatibility with DVD read-only systems,allowing playback in existing DVD players. Such write-once discs areprovided with guides called pregrooves. The pregroove wobbles slightlyin a radial direction of the disc around a central frequency, whereininformation such as a recording time address information called ATIP(Absolute Time In Pregroove) or a recording address information calledADIP (Address In Pregroove) are recorded with an FSK (Frequency ShiftKeying) modulation.

FIG. 1 shows a schematic block diagram of an optical disc recorderaccording to the preferred embodiments. In FIG. 1, input data DI issupplied to an optical unit 10 in order to be recorded or written to theoptical disc. On the optical disc, i.e. the DVD+R disc, a thin organicdye film is provided as a data storage layer. As already mentioned, therecording principle is based on irreversibly modifying properties of therecording layer to be inscribed. The digital information is contained inthe length of the recorded marks and unmodified spaces between them.Furthermore, a control unit 20 which may be any kind of processorcircuit is provided which controls the optical unit 10 in a manner so asto set individually selected recording speeds ν_(si) for each recordinglayer L_(i), wherein i=0 to n−1 and denotes a specific one of nrecording layers provided in the multi-layer optical disc. In case of adual-layer optical disc, two recording layers L0 and L1 are provided andthus n=2.

It is to be noted here that the block diagram of FIG. 1 only shows thoseparts of the recording apparatus which are involved in the power controlprocedure of the present invention, while other components which mightbe necessary for performing the recording operation have been omittedfor reasons of simplicity.

According to FIG. 1, the optical unit 10 is arranged to read and supply,e.g. among other disc parameters, a control information stored,recorded, embossed, or in another way written on the optical disc andindicating write strategy parameters including a set of individualrecording speeds ν_(i) for each recording layer L_(i) and theirassociated or related writing laser powers P_(i). As an example, thecontrol information which indicates the different write strategyparameters at different recording speeds can be stored as e.g. ADIPinformation on the dual-layer DVD+R disc.

According to the first preferred embodiment, the control unit 20determines and optionally stores the set of individual recording speedsν_(i) for each recording layer L_(i) and their associated or relatedwriting laser powers P_(i). Based on this information, the control unit20 can determine the highest recording speed for each of the recordinglayers, taken into account the maximum laser power of the opticalrecorder. The control unit 20 may store the determined set of individualrecording speeds ν_(i) for each recording layer L_(i) and theirassociated or related writing laser powers P_(i). The control unit 20then starts recording in the most sensitive recording layer at thehighest speed possible, taken into account the maximum laser power ofthe optical drive which may be stored at a corresponding storingfacility of the disc recorder. Typically, this recording layer will bethe top recording layer L₀ facing the optical unit 10. Once this toprecording layer L₀ has been fully recorded, the control unit 20 performscontrol so as to continue recording on the next most sensitive recordinglayer at the highest speed possible, i.e., the bottom layer L₁. In caseof a multi-layer disc with more than two recording layers, the recordingscheme will continue in the same manner by continuing recording on thenext most sensitive recording layer at the highest speed possible, andso on.

Hence, instead of determining an “overall recording speed” for theentire optical disc based on the maximum speed of the “slowest layer”,the top recording layer L₀ may be recorded at a higher speed than thebottom recording layer L₁. In this way, half of the storage capacity ofthe dual-layer disc may be recorded at a higher speed than the “overallrecording speed”. In practice, more than half of the storage capacitycan be recorded at a higher speed, since most often only part of theslowest layer, i.e. the bottom layer (L1), will be used. Clearly, theproposed multi-speed recording scheme can reduce the total time requiredto record a multi-layer optical storage medium compared to asingle-speed “overall” recording scheme.

FIG. 2 shows a specific example of a dual-layer DVD+R disc with specificwrite strategy parameters for different laser powers. The correspondingdual-layer DVD+R optical drive or optical recorder has a specificmaximum laser power of 35 mW. According to the control informationprovided on the dual-layer DVD+R disc, e.g., as an ADIP information,laser power values are specified for each recording layer for recordingat an indicated speed. The top recording layer L₀ can be recorded at arelative speed of 2.4× if the laser power is at least set to a value of24 mW. Additionally, the top recording layer L₀ can be recorded at ahigher relative speed of 4× if the laser power is at least set to avalue of 33 mW. On the other hand, the bottom recording layer L₁ can berecorded at a relative speed of 2.4× if the laser power is at least setto a value of 30 mW. Additionally, the bottom recording layer L₁ can berecorded at a higher relative speed of 4× if the laser power is at leastset to a value of 41 mW.

Consequently, in the specific case of recording on the optical discspecified in FIG. 2 and using a disc recorder with a maximum laser powerof 35 mW, the control unit 20 will apply a recording scheme in whichrecording starts on the top recording layer L₀ at 4× recording speed.Once this top recording layer L₀ has been fully recorded, the controlunit 20 controls the optical unit 10 so as to continue recording on thebottom layer L₁ at the lower 2.4× recording speed due to the fact that alaser power of 41 mW required for recording at the higher speed is notavailable.

FIG. 3 shows a schematic flow diagram of a recording or writingprocedure or mechanism according to the first preferred embodiment.

In step S101, the optical unit 10 initially reads control informationincluding disc parameters stored on the optical disc, e.g., as an ADIPinformation, and supplies the control information to the control unit20. Then, in step S102, the control unit 20 determines the maximum writepower specified for the disc recorder, and subsequently selects in stepS103 individual recording speeds ν_(si) for each of the recording layersL₀ and L₁ based on the determined maximum write power. In step S104 arunning parameter i is set to zero, to be able to know the position ornumber of the currently recorded or inscribed recording layer. Followingthis, in step S105, the control unit 20 starts the writing operation forthe top recording layer L₀ at the recording speed ν_(s0) selected forthe top recording layer L₀. In step S106, it is checked whether writinghas been finished before the top recording layer L₀ has been filled. Ifnot, i.e. if there is still data left for writing to the next layer, therunning parameter i is incremented in step S107 and the procedurereturns to step S105 in order to continue the writing operation on thesubsequent layer L₁ at the recording speed ν_(s1) selected for thissubsequent layer L₁. On the other hand, if it is determined in step S106that writing has been finished before the end of the current recordinglayer, the writing procedure ends.

In the above first preferred embodiment, the top recording layer L₀ issuggested to be fully recorded, e.g. at the highest speed, before anyrecording on the subsequent layer L₁ is started. However, as analternative solution according to a modification of the preferredembodiment which is specifically relevant for optical discs according tothe dual-layer DVD-ROM standard, it could be desirable to have an equalamount of data present on each of the two layers. That is, recording onthe subsequent recording layer L₁ of a dual-layer disc could alreadystart once half of the data has been written to the top recording layerL₀.

Furthermore, as another modification of the first preferred embodiment,a more optimum or better adapted recording speed, which corresponds to arecording power even closer to the maximum write power, may be obtainedor selected in the selection step S103 of FIG. 3 by interpolation orextrapolation of discrete numbers or values stored in the pre-groove. Ofcourse, other estimation procedures can be used for deriving theselected recording speed from the stored numbers or values.

In the foregoing, it has been assumed that the top layer is the mostsensitive layer, which can be recorded at a higher speed than the bottomlayer. However, there may be recording media or record carriers, wherethe opposite is true, i.e. the bottom layer is more sensitive than thetop layer. In such cases, the bottom recording layer will be recorded ata higher recording speed, while the top recording layer is recorded at arelatively lower recording speed.

According to a second preferred embodiment, the recording sequence ororder of the recording layers is determined based on the sensitivity ofeach layer and thus based on the associated maximum recording speed.This is specifically advantageous for recording media consisting ofthree or more recording layers, where the order of layer sensitivity notnecessarily corresponds to the order of layers with respect to theoptical unit 10. As an example which corresponds to the recordingsequence of the first preferred embodiment, the recording layer with thehighest sensitivity, which thus allows the highest recording speed, maybe recorded first, followed by the recording layer with the secondhighest sensitivity, and so on. Of course, other sequences could beimplemented based on desired characteristics of the application.

The general structure of the optical disc recorder according to thesecond preferred embodiment is similar to the first preferred embodimentas depicted in FIGS. 1 and 3. Therefore, a description of the identicalparts is omitted here for reasons of brevity. However, the modificationaccording to the second preferred embodiment requires an additionalordering step S103 a in the flow diagram of FIG. 3, which can beintroduced between steps S103 and S104. In the newly introduced stepS103 a, the original sequence of the recording layers Li as arranged onthe disc is re-ordered based on the individual recording speeds selectedin step S103. The re-ordered sensitivity-based sequence L1 to Ln ofrecording layers is then processed similar to the first preferredembodiment in the loop consisting of steps S106 and S107 of FIG. 3,wherein the control unit 20 is arranged to control the optical unit 10in such a manner that recording is effected on the selected recordinglayer at the selected recording speed.

As an alternative, the individual sensitivities may be directly obtainedfrom a control information written on the optical disc, as a discparameters which can be read in step S101 of FIG. 3. In this case, there-ordering in step 103 a can be performed directly based on the readsensitivity parameters.

In summary, a recording apparatus and method is proposed for recordingdata on at least two layers of a recording medium by using a radiationpower, wherein individual recording speeds are determined for respectiveones of the at least two layers at different values of the radiationpower. A recording speed to be used for recording on an individual oneof the at least two recording layers is selected based on a maximumradiation power specified for the recording operation, and the speed ofthe recording operation is controlled individually for each of the atleast two layers based on the selected recording speed. Thedetermination of the individual recording speeds at different radiationpower values may be written or embossed on a record carrier.Furthermore, the recording sequence used for recording on the recordinglayers may be set based on the sensitivities and thus recording speeds.Thereby, total recording time can be minimized for multi-layer recordingmedia.

It is noted that the present invention is not restricted to the abovepreferred embodiment but can be used in any recording scheme so as toreduce the required recording time. In particular, the present inventionis not restricted to optical disc media, but can be used for anyrecording media having the different writing properties for differentrecording layers, which require different radiation powers and relatedrecording or writing speeds. Furthermore, any type of controlinformation suitable for predicting or determining a required recordingspeed in relation to the radiation power can be stored on the recordingmedia or at the recording apparatus. The preferred embodiments may thusvary within the scope of the attached claims.

The invention claimed is:
 1. A recording apparatus comprising: means forreading a record carrier, said recording carrier having at least tworecording layers (L0, L1) for recording data using a radiation power,said record carrier having written thereon a control information whichindicates individual recording speeds to be used for respective ones ofsaid at least two recording layers at different values of said radiationpower; means for selecting a highest available recording speed andradiation power for a selected one of said at least two layers based onan available radiation power and said control information; and means forwriting data to said selected one of said two employing said highestavailable recording speed and radiation power.
 2. The apparatusaccording to claim 1, wherein said control information is pre-stored ina pre-groove of said record carrier.
 3. The apparatus according to claim1, wherein said record carrier is one selected from a group of opticaldiscs consisting of: dual-layer DVD+R, dual-layer DVD+RW, dual-layerDVD-R and dual-layer DVD-RW.
 4. An apparatus comprising: means forreceiving a record carrier having at least two recording layers (L0, L1)for recording data by using a radiation power, said record carrierhaving written thereon a control information which indicates individualrecording speeds to be used for respective ones of said at least tworecording layers at different values of said radiation power; and acontrol unit configured to: read said control information; determine anindividual recording speed and radiation power for selected ones of saidat least two layers based on said control information; adjust saiddetermined individual recording speed and radiation power to be ahighest available recording speed based on an available radiation power,and write data to a selected one of said layers of said record carrierwith said highest available recording speed.
 5. An apparatus accordingto claim 4, wherein said control information is pre-stored in apre-groove of said record carrier.
 6. An apparatus according to claim 4,wherein said record carrier is one selected from a group of opticaldiscs consisting of: DVD+R, DVD+RW, DVD-R and DVD−RW.